[PATCH tip/core/rcu 09/13] locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe

[Paul E. McKenney]

From: Oleg Nesterov <oleg@xxxxxxxxxx>

This is the temporary ugly hack which will be reverted later. We only
need it to ensure that the next patch will not break "change sb_writers
to use percpu_rw_semaphore" patches routed via the VFS tree.

The alloc_super()->destroy_super() error path assumes that it is safe
to call percpu_free_rwsem() after kzalloc() without percpu_init_rwsem(),
so let's not disappoint it.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/locking/percpu-rwsem.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index e2621fbbcbd1..9529a30ec57b 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -26,6 +26,13 @@ EXPORT_SYMBOL_GPL(__percpu_init_rwsem);
 
 void percpu_free_rwsem(struct percpu_rw_semaphore *brw)
 {
+	/*
+	 * XXX: temporary kludge. The error path in alloc_super()
+	 * assumes that percpu_free_rwsem() is safe after kzalloc().
+	 */
+	if (!brw->fast_read_ctr)
+		return;
+
 	free_percpu(brw->fast_read_ctr);
 	brw->fast_read_ctr = NULL; /* catch use after free bugs */
 }
-- 
2.5.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/